Autoimmune diseases distinguish themselves by the occurrence of autoantibodies, i.e., antibodies directed against constituents of the own organism. Autoantibodies may induce damage of the organism, an organ or part of an organ thus triggering partially serious life-threatening diseases. The origination of such a disease is due to differing pathogenic mechanisms such as neutralization of antigens, e.g., hormones, blocking or stimulation of a receptor for biological active substances, e.g., autoantibodies active against the receptor of the thyroid-stimulating hormone in the case of hyperthyreosis, binding to certain cell or tissue structures accompanied by the induction of a complement-mediated inflammation, e.g., glomerulonephritis, antiautobodies active against glomerulus basement membranes. Tissues damage may also be induced by cell-mediated mechanisms (autoantibody-dependent cellular cytotoxicity) or by localized and systemic immune complex deposits after the binding of the autoantibodies to soluble antigens.
In addition to such obviously directly damaging autoantibodies, a plurality of autoantibodies active against blood, cell or tissue constituents occur in man, to which a tissue-damaging part cannot be assigned yet clearly by now. The group of rheumatic diseases, particularly the inflammatory rheumatic diseases to which the collagen diseases are attributed, is characterized by the occurrence of numerous autoantibodies. They react, e.g. with antigens of the cell nucleus such as double-stranded DNA, single-stranded DNA, RNA, histones, non-histone proteins, ribonucleoproteins, chromosome-associated antigens, e.g., centromeres or spindle apparatus, or with antigens which are expressed only in certain phases of the cell cycle, e.g., cycline.
The above autoantibodies are found in the case of diseases such as lupus erythematodes, Sjogren's syndrome, mixed connective tissue disease, polymyositis, dermatosclerosis, CREST syndrome, Wegener's granulomatosis and dermatomyositis. They are usually detected by reaction with nuclear extracts from thymocytes of calves or rabbits. Due to this, a differential diagnosis of these diseases, particularly of dermatomyositis, is, however, not possible. But such a diagnosis is a precondition for the selection of treatment.
Therefore, it is the object of the present invention to provide means by which dermatomyositis can be detected by way of differential diagnosis.